An unwavering goal of contemporary vehicle designers is the achievement of increased fuel efficiency, i.e., reduced fuel consumption. Designers of passenger cars, light trucks and long haul tractor trailers continually strive to improve the fuel efficiency of their vehicles while addressing other operating and performance parameters. While recent fuel consumption reductions stated in percent of hybrid vehicles are impressive, much smaller percentage fuel consumption reductions when applied to long haul tractor trailers typically represents much larger actual savings in fuel consumption because such vehicles consume more fuel on a miles per gallon basis and are driven many miles farther during any given period of time, for example, a year.
One of the improvements to long haul tractor trailers in recent years is the automated mechanical transmission. In this device, a relatively conventional multiple speed (gear ratio) heavy duty transmission includes an actuator assembly which is controlled by a master controller or microprocessor. The microprocessor includes a plurality of inputs which receive signals from various sensors such as speed sensors, a throttle position sensor, brake and ABS sensors, a shift selector, an operator controlled mode selector and other devices and, through the use of algorithms, computational routines, look-up tables and the like, controls operation of the master clutch and selection and engagement of transmission gears. Because such systems will consistently command upshifts and downshifts based upon the sensed conditions and established shift rules, fuel efficiency of such devices is generally good.
The fuel efficiency (consumption) of a particular engine, i.e., a particular size or output engine from a particular manufacturer, may be presented in a fuel efficiency map. This map relates fuel consumption as a function of engine speed, delivered torque and delivered horsepower. The fuel map includes a plurality of isograms or isolines of constant fuel consumption which are roughly arranged about a single value of speed and torque, i.e., a point, of maximum fuel efficiency. Stated somewhat differently, a single, vehicle operator or a single shift program when used with two engines having distinct fuel efficiency maps will be unable to achieve optimum fuel efficiency with both and may perform at a fuel efficiency well below that which could be obtained by commanding shifts based upon the fuel efficiency map of the given engine to achieve optimum fuel efficiency.
Different styles and designs of internal combustion engines and engines from different manufacturers have different fuel efficiency maps. Accordingly, if a truck or tractor manufacturer utilizes two or more different engines in a particular truck, the experience and habits of one operator utilizing a manual transmission or an automated mechanical transmission with the same control algorithm and operating logic will not provide optimum fuel efficiency in both trucks.
Such automated mechanical transmissions often have multiple control modes such as fully automatic and manual. The fully automatic mode may include several sub-modes that emphasize, that is, more heavily weight, one control variable or parameter over others. For example, one automatic control mode may emphasize performance, while another may provide improved control at very low vehicle speeds while a third may seek to minimize shifting by utilizing more widely separated upshift and downshift values.
The present invention is directed to further improving the fuel efficiency of multiple speed mechanical and automated mechanical transmission engine combinations.